RENO, Nev. (AP) -- The National Transportation Safety Board has concluded that a distracted driver in a truck with bad brakes was the probable cause of a fiery collision with an Amtrak passenger train that left six dead in northern Nevada last year.

On a 5-0 vote, the panel also agreed Tuesday that insufficient strength of passenger car walls likely contributed to the number of deaths and more than a dozen injuries after the truck skidded 300 feet into the train on June 24, 2011.

NTSB investigators said the truck driver killed in the crash apparently didn't notice the train because he was fatigued as a result of inconsistent sleeping patters, was suffering from ankle pain or possibly could have been checking messages on his cellphone. But the panel decided there wasn't enough evidence of any of those things to include in the formal probable cause finding issued in Washington.

Time-lapse photography presented to the panel Tuesday showed the guard crossing gate fully extended well before the fiery crash.

NTSB's preliminary findings in September offered conflicting accounts of whether the guard crossing arm operated properly or whether the truck driver just wasn't paying attention. But the photos showed the gate was in place 4 seconds before impact and monitoring equipment indicated the warning lights were flashing and the gate in place 18 seconds before the collision when the truck was still 900 feet away from the crossing.

"There are two key things we know about what happened," NTSB Chairman Deborah Hersman said during Tuesday's hearing in Washington.

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"One, the driver had plenty of opportunity to observe and react to the lights and gates at the crossing before the arrival of the Amtrak train. Two, we know the truck had faulty equipment -- brakes that were not properly maintained," she said.

The California Zephyr bound from Chicago to Emmeryville, Calif., was three hours behind schedule when it left Salt Lake City on June 24, 2011.

It was going 77 mph in northern Nevada's Forty Mile Desert just south of U.S. Interstate 80 and approaching the crossing at U.S. Highway 95 north of Fallon when the engineer noticed that a semi-truck hauling two open empty trailers didn't seem to be slowing for the oncoming train, according to the NTSB's preliminary findings.

With the whistle blaring, the train's engineer initiated the emergency brakes about 450 feet from the crossing. Rubber skid marks on the highway show the truck driver hit his brakes 300 feet from the tracks but skidded nearly the length of a football field into the side of the train, investigators said. If the brakes had been properly maintained, the truck should have stopped within about 230 feet of breaking, they said.

NTSB investigator Jana Price said there were no obstructions to the driver's view or any glare at the time that would have prevented him from seeing the crossing gate and lights.

She said they do not know why he didn't stop sooner, although he may have been fatigued due to inconsistent sleep patterns and could have been distracted by ankle pain he had been suffering from.

Board member Robert Sumwalt said he found it "phenomenal" that the driver didn't react to the crossing warning sooner.

"I cannot imagine barreling down the highway at 60 mph and wait until you are less than the length of a football field before applying the brakes," he said. "This accident could have been avoided if the driver would have applied brakes 1.4 seconds sooner or if John Davis Trucking would have maintained the brakes as they should have been maintained."

The truck embedded in the side of a crew car, which ultimately was destroyed by the fire that also charred a passenger car behind it. The debris field stretched 150 feet west along the tracks and the engine finally screeched to a halt another 3,000 feet away.

The children of the conductor who died in the crash, Laurette Lee, 68, of South Lake Tahoe, Calif., are among those who have sued over the crash, naming the late truck driver, Larry Valli, 43, and his employer, John Davis Trucking Co. of Battle Mountain, Nev. as defendants.

NTSB investigator Jennifer Morrison said 11 of the truck trailer's 16 brake drums were worn beyond limits. She said tests conducted by the Nevada Highway Patrol also found nine of the 16 brakes were out of adjustment or inoperative, but she said the patrol didn't use the proper test guidelines so it was not possible to tell for sure if those results were entirely accurate.

Those conditions might not have been obvious to the driver, who likely would not have known his brakes were faulty unless he'd been required to make a quick stop before, she said.

However, NTSB also discovered the warning lights and anti-lock brake system had been disconnected and the wiring gathered in a loop for an unknown reason.

"They were deliberately cut and tied up and disconnected," Morrison said.

The NTSB investigation found Valli had been cited for 10 speeding violations over the past 10 years. He had been talking on a cellphone earlier in the day but apparently not at the time of the crash, the NTSB said.

The passengers killed in the accident were: Cheuy Ong, 34, of West Jordan, Utah; Francis Knox, 58, and Karly "Annie" Knox, 18, of Seward, Neb.; and Barbara Bell, 60, of United Kingdom.